This invention relates to gas insulated circuit breakers having a closing resistor switch therefor which has a high resistivity and has the ability to withstand high voltage accompanying the closing of the circuit breaker contacts.
The utilization of gas high voltage insulated circuit breakers in substation installations in recent years has resulted in smaller, more compact circuit breaker enclosures without a decrease in the voltage rating and often with a voltage rating increase. Thus, the smaller envelope and higher voltage rating requires compact components so as to provide adequate insulating spacing from other components and also from the envelope itself. These more compact components, however, must provide the necessary function for which they are intended.
When the interrupter contacts of a circuit breaker are closed voltage surges are experienced. To dampen the overvoltage on the line it is well known to preinsert a resistance in the circuit during the closing operation just prior to the closing of the interrupter contacts. This is shown in U.S. Pat. No. 3,291,947 and U.S. Pat. No. 3,390,239 as well as in a paper published in the IEEE Transactions on Power Apparatus and Systems, December 1964, -- Switching of EHV Circuits, II -- Surge Reduction with Circuit Breaker Resistors -- by Hedman et al.
The circuit breaker which incorporates the present invention includes an enclosure filled with an insulating gas at a relatively low pressure. Within the enclosure are several serially connected main interrupters. A resistor switch is associated with each interrupter and is connected to shunt the contacts thereof. Each resistor switch comprises a pair of relatively movable contacts operable to electrically connect a plurality of parallelly connected segmental resistor stacks into the shunt connection to thereby withstand the high voltage surge present at interrupter closing. These resistor switches must be contained and protected by the shielding arrangement provided for the interrupters. However, with presently known resistors to provide the resistivity necessary to withstand the high voltage stresses experienced with 345 Kv to 550 Kv or higher rated circuit breakers these known resistors would have to be exceedingly long to provide the necessary resistance. With the limited space available within the interrupter enclosure and between the interrupter shields, a long resistor switch cannot be utilized.